338 resultados para burrows
Resumo:
The atmospheric chemistry of iodine and bromine in polar regions is of interest due to the key role of halogens in many atmospheric processes, particularly tropospheric ozone destruction. Bromine is emitted from the open ocean but is enriched above first-year sea ice during springtime bromine explosion events, whereas iodine is emitted from biological communities hosted by sea ice. It has been previously demonstrated that bromine and iodine are present in Antarctic ice over glacial-interglacial cycles. Here we investigate seasonal variability of bromine and iodine in polar snow and ice, to evaluate their emission, transport and deposition in Antarctica and the Arctic and better understand potential links to sea ice. We find that bromine enrichment (relative to sea salt content) and iodine concentrations in polar ice do vary seasonally in Arctic snow and Antarctic ice and we relate such variability to satellite-based observations of tropospheric halogen concentrations. Peaks of bromine enrichment in Arctic snow and Antarctic ice occur in spring and summer, when sunlight is present. Iodine concentrations are largest in winter Antarctic ice strata, contrary to contemporary observations of summer maxima in iodine emissions.
Resumo:
A biostratigraphically continuous, but intensely bioturbated, Cretaceous/Tertiary boundary sequence was cored during Ocean Drilling Program (ODP) Leg 113 on Maud Rise (65°S) in the Weddell Sea off East Antarctica. This interval is the first recovered by ODP/DSDP in the South Atlantic sector of the Southern Ocean and offers a unique opportunity to study the nannofossil sequences leading up to and beyond the terminal Cretaceous event at a high southern latitude. The K/T boundary lies just within Chron 29R and is placed at ODP Sample 113-690C-15X-4, 41.5 cm. An iridium anomaly was independently noted at about this level as well. Upper Maestrichtian-lower Paleocene sediments consist mostly of light-colored nannofossil chalks. Dark brown sediments at the base of the Danian (Zone CPla) are characterized by an increased clay content attributed to a drop in calcareous microplankton productivity following the terminal Cretaceous event. Although delineation of the boundary is hampered by intense bioturbation, the sharp color contrast between overlying clay-rich, dark brown chalks of the Tertiary and light cream colored chalks of the Cretaceous aids in the selection of the K/T horizon. Several dark colored burrows sampled at intervals as far as 1.3 m below the boundary and within the light colored Cretaceous chalk were found to contain up to 17% Tertiary nannofossils. Calcareous nannofossils from the boundary interval were divided into three groups for quantitative study. The three groups, "Cretaceous," "Tertiary," and "Survivor," exhibit a sequential change across the boundary with the Cretaceous forms giving way to a Survivor-dominated assemblage beginning at the boundary followed shortly thereafter by the appearance of the Tertiary taxa, Cruciplacolithus and Hornibrookina. The species, H. edwardsii, comprises nearly 50% of the assemblage just above the Zone CPla/CPlb boundary, an abundance not reported elsewhere at this level. Calculation of individual species abundances reveals several additional differences between this K/T boundary interval and those studied from middle and low latitude sections. The percentage of Thoracosphaera is much lower at the boundary in this section and a small form, Prediscosphaera stoveri, is extremely abundant in Cretaceous sediments just below the boundary.
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Back Row: Russ Miller, Jon Falk, Chuck Ritter, Larry Barros, Lou Kovacs, John Ferens, Dave Garlow
9th Row: Fritz Seyferth, Gerald Ingram, Jerry Meter, Tirrel Burton, Lloyd Carr, Jerry Hanlon, Gary Moeller, Paul Schudel, Elliott Uzelac, Milan Vooletich, Bob Thornbladh, Alex Agase, Bill Giarmo, Joe English, Cam Cameron, Mike Gittleson
8th Row: Sean Guffey, John Zingales, Garret Smith, Don Lessner, Trey McNeil, Brad Burrows, Bob Wood, Kyle Anderson, Ernie Bock, Mike DeBoer, Rick Sutkiewicz, Joh Duerr, Monte Robbins, Phil Logus, Dave Mandel
7th Row: Bob Stites, Patrick Fitzgerald, Dave Howe, Dave Dever, Bob Cernak, Ernie Holloway, John Willingham, Mark Hill, Chris D'Esposito, Mike Husar, Rick Masters, James Brown, Rick Stites, Scott Mandel, Ken Mouton, Phil Wentworth
6th Row: Jamie Morris, Dan Holloway, John Vitale, Mike Dames, Bob Tait, Mark Erhardt, Mike Kovac, Chuck Adams, Dave Chester, Bud Gereg, Mark Messner, Dave Herrick, Keith Evans, Erik Campbell, John Whitledge
5th Row: Doug Mallory, Gene Lawson, Tim Schulte, Todd Schulte, Andre McIntyre, Carlitos Bostic, John Elliott, Andy Borowski, Paul Jokisch, Steve Thiebert, Jack Walker, Gene Cecchini, David Folkertsma, Billy Harris, John Balourdos
4th Row: Ed Hood, Al Bishop, Ken Higgins, Keith Cowan, Rick Fraser, John Mihic, Jerry Quaerna, Mike Reinhold, Marty Shimko, Garland Rivers, Gerald White, Chris Zurbrugg, Phil Webb, Russ Rein, Pat Moons
3rd Row: Steve Johnson, Ben Logue, Gilvanni Johnson, Greg Randall, Mike Krauss, Bob Perryman, Mark Hammerstein, Jim Harbaugh, Dieter Heren, Paul Schmerge, Triando Markray, Andy Moeller, Eddie Garrett, Thomas Wilcher, Ivan Hicks
2nd Row: Tony Gant, John Ghindia, Bob Popowski, Bob Tabachino, Joe Gray, Jeff Akers, Kevin Brooks, Eric Kattus, Mike Mallory, Brad Cocharn, Jim Scarcelli, Phil Lewandowski, Dave Simon, Mike Sessa, Mike Melnyk
Front Row: Todd Schlopy, Mike Hammerstein, Art Balourdos, Clay Miller, Rodney Lyles, Sim Nelson, Doug James, Al Sincich, Vince Bean, Vince DeFelice, Dave Meredith, Greg Armstrong, Nate Rodgers, Tim Anderson, Bob Bergeron, Head Coach Bo Schembechler.
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Back Row: James Brown, Jon Falk, Dave Garlow, Bill Sheridan, Tom Hassel, Reggie Mitchell, Sr. Mgr. Michael Drews, Bob Tait, Pete Wentworth, Russ Miller, Larry Barrows, John Ferens, Chuck Ritter
11th Row: Paul Alexander, Alex Agase, Bob Thornbladh, Tirrel Burton, Jerry Hanlon, Elliot Uzelac, Gary Moeller, Milan Vooletich, Jerry Meter, Lloyd Carr, Cam Cameron, Michael Trgovac
10th Row: Fritz Seyferth, Andy Johnson, John Althouse, Joel Boyden, Mike Gillette, Mike Edwards, Sean LaFountaine, Olatide Ogunfitidimi, Vincent Washington, Steve Woroniecki, Gulam Kahn, Mike Gittleson
9th Row: John Kolesar, David Weil, Scott Crawford, Chris Simmons, Brian Reid, John Plantz, Mike DePalma, Keith Mitchell, Keith Cooper, Joe Holland, Frank Petroff, Anthony Mitchell, Bob Hurst
8th Row: Mike Taylor, Demetrius Brown, Dave Arnold, Mike Jones, Brent White, Pat Olszewski, John Herrman, Jeff Brown, Bobby Abrams, Derrick Walker, J.J. Grant, Rick Hassel, Cliff Dochterman
7th Row: Ernie Bock, Kyle Anderson, Mike DeBoer, John Duerr, Scott Mandel, Dave Mandel, John Whitledge, Brad Burrows, Don Lessner, Pat Fitzgerald, Geoff Bissell, Rick Sutkiewicz, Phil Logas
6th Row: Ernie Holloway, Jamie Morris, John Zingales, Chuck Adams, Chris D'Esposito, Mark Erhardt, John Vitale, Dave Dever, John Willingham, Bob Cernak, Rick Stites, Bob Stites
5th Row: Gene Lawson, Ken Mouton, Erik Campbell, Dave Chester, Michael Dames, Mike Husar, Dave Herrick, Mark Hill, Dan Holloway, Mike Kovac, Mark Messner, Keith Evens
4th Row: Ed Hood, Tim Schulte, Ken Higgins, Steve Thibert, Phil Webb, Carlitos Bostic, David Folkertsma, Andy Borowski, Monte Robbins, Todd Schulte, Jack Walker, Russell Rein
3rd Row: Pat Moons, Marty Shimko, Andre McIntyre, Garland Rivers, Dan Rice, John Mihic, John Elliott, Gerald White, Chris Zurbrugg, Billy Harris, Keith Cowan, Doug Mallory
2nd Row: Ben Logue, Greg Randall, Mark Hammerstein, Dieter Heren, Gilvanni Johnson, Paul Jokisch, Mike Reinhold, Jerry Quaerna, Mike Krauss, Andy Moeller, Paul Schmerge, Thomas Wilcher, Coach Bo Schembechler
Front Row: Tony Gant, Bob Perryman, Bob Tabachino, Jeff Akers, Brad Cochran, Mike Mallory, Mike Hammerstein, Eric Kattus, Clay Miller, Jim Scarcelli, Jim Harbaugh, Ivan Hicks
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Transportation Systems Center, Cambridge, Mass.
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Mode of access: Internet.
